Neuroblastoma is a cancer arising from autonomic neuron progenitor cells that occurs in the adrenal medulla or as paraspinal tumors in the abdomen or thorax of infants and young children. If it is identified in children over the age of 1, it is nearly always a highly malignant, aggressive cancer that kills the child within 4-5 years, even after a strenuous chemotherapeutic regimen combined with radiation and a bone marrow transplant. This project will determine whether an unusual nicotinic acetylcholine receptor is a novel target for therapeutics in treating neuroblastoma. We have isolated cells from bone marrow aspirates obtained from patients with stage 4 neuroblastoma. When tested in xenograft assays in immunodeficient mice, the cells can be categorized into tumor-initiating cells (TICs) and non-tumor initiating cells (non-TICs). We have discovered that the gene encoding the a5 nicotinic acetylcholine receptor (nAChR) subunit, CHRNA5, is expressed at 7- 19-fold higher levels in TICs than in non-TICs. Furthermore, CHRNA5 is 2-10-fold higher in TICs than in normal neurogenic neural crest stem cells, and CHRNA5 is elevated in primary neuroblastoma tumors and cell lines derived from tumors (SH-SY5Y, SKN-KCN, SKN-KCNR) above levels found in normal sympathetic ganglia. In a high throughput drug screen for compounds that would reduce proliferation of TICs, MG 624, a nAChR antagonist, was identified. Based upon our expression data, we hypothesize that nicotinic receptors containing a5 contribute to the malignant phenotype of neuroblastoma and therefore may be a new target for drugs because these receptors are uncommon in the normal autonomic nervous system. The proposed aims will test this hypothesis by: 1) using RNAi to determine whether one or more nAChR subunits is necessary for the malignant phenotype of neuroblastoma cells (TICs and cell lines from primary tumors) and their sensitivity to MG 624; 2) determining whether overexpression of CHRNA5 and/or other subunits in normal skin-derived precursors is sufficient to produce a transformed phenotype.